A prior art irradiation system that utilizes a conveyor system for transporting articles through a target region is described in U.S. Pat. No. 5,396,074 to Peck at el. U.S. Pat. No. 5,396,074 is assigned of record to the assignee of record of this application. In such prior art system, the radiation source and the conveyor system are disposed in a room having concrete walls, wherein such concrete walls and additional concrete walls defining an angled passageway to the room shield loading and unloading areas located outside of the room from radiation derived from the radiation source.
A system for reorienting the articles from retransportation through the target region also is described in U.S. Pat. No. 5,396,074 to Peck et al. In such reorienting system, a gear rack is disposed adjacent a reroute conveyor system (or bridging arrangement) that transports the articles from a position on a primary conveyor system located past the target region in the direction of movement of the primary conveyor system to a position on the primary conveyor system located before the target region in such direction of movement. A rotatable collar mechanism on an article carrier interacts with the gear rack in such a manner as the article carrier is being transported past the rack by the reroute conveyor system as to reorient the article carrier by 180 degrees.
In co-pending application 08/854,202 filed in the USPTO on May 9, 1997, and assigned of record to the assignee of record of this application, an article irradiation system is provided comprising a radiation source positioned for scanning a target region with radiation, a conveyor system for transporting articles from a loading area through the target region to an unloading area, and radiation shielding material defining a tunnel which closely encompasses portions of the conveyor system extending away from the target region toward the loading and unloading areas. By so disposing such closely encompassing radiation shielding material in order to shield the loading and unloading areas from radiation derived from the radiation source, an irradiation system is provided that requires a significantly less overall area than in the prior art.
For example, in the system of co-pending application Ser. No. 08/854,202 the conveyor system is disposed in a path having turns closely encompassed by the radiation shielding material and of such degree between the target region and the loading and unloading areas that the radiation shielding material closely encompassing said turns precludes a direct line of sight between the target region and the loading area and a direct line of sight between the target region and the unloading area. As a result, the loading and unloading areas in the system disclosed and claimed in co-pending application Ser. No. 08/854,202 are shielded from radiation derived from the radiation source. Such disposition facilitates a compact embodiment of the irradiation system in which the loading area and the unloading area are within a common unshielded area and the path of the conveyor system defines a closed loop from the loading area to the unloading area. Such disposition also facilitates a compact embodiment of the irradiation system in which the conveyor system is included in an assembly line having an unshielded loading area and an unshielded unloading area.
In a second aspect, the article irradiation system disclosed and claimed in co-pending application Ser. No. 08/854,202 comprises a radiation source positioned for scanning a target region with radiation and a first conveyor system for transporting articles from a loading area through the target region to an unloading area, with the first conveyor system being disposed in a closed-loop path. A first side of the article is irradiated by the radiation source during the movement of the articles by the first conveyor system through the target region. The system of co-pending application Ser. No. 08/854,202 further comprises a second conveyor system coupled to the first conveyor system for transporting the articles from a first position on the first conveyor system. The first position is past the target region and has a given alignment. The second position on the first conveyor system is before the target region and has an alignment that is 180.degree. different than the given alignment. In this way, the articles transported by the first conveyor system are reoriented by 180.degree. with respect to the path of the first conveyor system for retransportation through the target region. This causes a second side of the articles to be irradiated by the radiation source during a second movement of the articles through the target region.
For example, in an embodiment of the system in co-pending application Ser. No. 08/854,202, the path of the first conveyor system has four turns and a straight segment between each pair of adjacent turns. The target region is within a first straight segment of the first conveyor system. The loading and unloading areas are adjacent a second straight segment of the first conveyor system on the opposite side of the loop from the first straight segment. The first position on the first conveyor system is in a third straight segment which is between the two turns of the loop that are between the target region and the unloading area. And the second position on the first conveyor system is in a fourth straight segment which is between the two turns of the loop that are between the target region and the loading area. In such an arrangement, the second conveyor system may be so simple as to merely defined a straight path from the first position on the first conveyor system to the second position on the first conveyor system.
In a third aspect, the system of co-pending application 08/854,202 provides a set of shielding modules for use in an article irradiation system that includes a radiation source positioned for scanning a target region with radiation and a conveyor system for transporting articles through the target region. These shielding modules comprise radiation shielding material which define a tunnel for closely encompassing a portion of the conveyor system. Such shielding modules are particularly well suited for use in embodiments of the irradiation system according to the above-described first aspect described above in which the conveyor system is disposed in a path having turns. For example some of the modules may be curved for respectively encompassing segments of the conveyor system having an arc of curvature that is an integer divisor of ninety degrees.
In a fourth aspect, the system of co-pending application Ser. No. 08/854,202 provides a radiation shielding assembly for use in an irradiation system that includes an electron beam radiation source positioned for scanning articles with an electron beam disposed in a target region. The radiation shielding assembly may comprise a beam stop of material for absorbing electrons and for converting the energy of the absorbed electrons into gamma-rays that are emitted from the beam stop. The beam stop is disposed on the opposite side of the target region from the radiation source. The radiation shielding assembly may also comprise a radiation shield for absorbing radiation while inhibiting emission of neutrons beyond the shielding assembly. The radiation shield defines a corridor through which the electron beam is scanned for irradiating articles disposed in the target region and further defines a tunnel through which articles may be transported to and from the target region. The tunnel and the corridor communicate with each other. When the corridor is positioned to communicate with the target region, one side of the article passing through the tunnel is irradiated with the radiation from the source.
The beam stop is disposed within a recess in a portion of the radiation shield that defines a portion of the corridor on the opposite side of the target region from the target source. In this way, gamma rays emitted from the beam stop toward the radiation source but obliquely thereto are inhibited by said portion of the radiation shield from entering the tunnel.